Prognosis of hepatoma is extremely poor, because recurrence is observed at a yearly ratio of about 25% after therapeutic treatment. Accordingly, one of outstanding important objects is prevention of recurrence of hepatoma, as well as early detection and therapy of hepatoma. (2E,4E,6E,10E)-3,7,11,15-Tetramethyl-2,4,6,10,14-hexadecapentaenoic acid (hereinafter sometimes abbreviated as “NIK-333” in the specification) is known as a compound having effects on delay or prevention of recurrence after therapeutic treatment of hepatoma. Muto et al. reported that, throughout a one-year oral administration of NIK-333 to patients after therapeutic treatment of hepatoma, the compound was revealed to have a high safety and suppress recurrence of hepatoma, thereby increased survival rate of the patients (New Eng. J. Med., 334, 1561, 1996; New Eng. J. Med., 340, 1046, 1999).
However, NIK-333 is unstable under light, heat, or oxygen, and susceptible to oxidation. Therefore, various techniques are required for preparation of pharmaceuticals. Including lipophilic vitamins as typical examples, most of lipophilic medicaments are unstable under light and heat and susceptible to oxidation, and thus various stabilization techniques are known for preparation of pharmaceuticals comprising these medicaments. As for preparation of pharmaceuticals comprising NIK-333, a method wherein a polyprenyl compound is dissolved in peanut oil to prepare a solution is disclosed in Japanese Patent Publication (Kokoku) (Sho) No 63-32058 (1988), and a pharmaceutical preparation formulated by filling NIK-333 together with peanut oil into a capsule is disclosed in Japanese Patent Unexamined Publication (Kokai) No 10-167960(1998). However, the pharmaceutical preparations obtained by these methods still have a problem of instability and are not satisfactory for a practical use.